Maritime Mobile Service Identity (MMSI)

A unique nine-digit number assigned to a vessel, coast station, or group of stations for digital communication and identification in the Global Maritime Distress and Safety System (GMDSS).

Maritime Mobile Service Identity (MMSI) is a critical component of modern maritime communication systems, enabling efficient and precise identification of vessels and stations during radio communications. This unique nine-digit number is assigned by national telecommunications authorities and is used in conjunction with Digital Selective Calling (DSC) and the Automatic Identification System (AIS). MMSI numbers are structured to include a country code, which identifies the nation of registration, followed by a series of digits unique to the vessel or station.

The MMSI system is integral to the Global Maritime Distress and Safety System (GMDSS), a framework designed to enhance safety and facilitate rescue operations at sea. By using MMSI, vessels can send distress alerts, communicate their position, and exchange information with other ships or shore stations with minimal risk of misidentification. For example, in an emergency, a DSC-enabled VHF or MF/HF radio can transmit a distress signal that includes the vessel’s MMSI, allowing search and rescue authorities to quickly identify and locate the vessel in distress.

In addition to safety functions, MMSI is also used for routine communication and navigation purposes. It enables vessels to exchange information automatically via AIS, such as position, course, and speed, improving situational awareness and collision avoidance. The system is a cornerstone of modern maritime operations, ensuring that communication remains reliable, efficient, and secure.